I know what the problem is. The way they make the TEZ easier to load, is by making the sabot thinner. If you don't watch it, your bore will start collecting plastic, which creates a layering of plastic over powder residue, over plastic and so on. Then, it becomes a little rough, even though your cleaning patches come out looking clean.
Combine a rough built up bore surface with the thin blue sabots, and you have loss of accuracy due to the disintegrating sabots.
Clean it with a plastic solvent, either shotgun wad remover, or acetone (slower), and JB bore compound or Remington Bore Cleaner (slower) and replace those blue sabots with MMP 12, or Harvester EZ Load sabots, whichever gives you best results.